The invention relates to a hydraulic motor to intermittently rotate a crank shaft by means of a plurality of hydraulic cylinders. More particularly, the invention relates to a hydraulic motor which rotates a crank shaft smoothly and intermittently for very certain angles.
There have been several intermittent rotation mechanisms, such as the combination of a rack and pinion, the combination of hydraulic cylinders and connecting arms, and a direct connection to an oil motor. They involve many problems to be solved, among which the most desirable one is to moderate the shock of stopping. And for such purpose, slow-down valves are employed or some devices are incorporated to the hydraulic oil circuit. Any complete solution on this problem to eliminate the shock of stopping and absorb the inertia of rotation, however, has never been proposed. So that, complicated hydraulic circuits or expensive valves are used for this purpose.
In the meantime, there is known a radial piston-type hydraulic motor in which a plurality of hydraulic cylinders are provided on the radial directions in the casing, and the crank shaft is rotated by pistons in the cylinders and connecting rods contacted to the eccentric portion of the crank shaft. The hydraulic oil pressure is provided to said hydraulic cylinders in turn, thus continuous rotation is caused by the hydraulic oil pressure. In this type of hydraulic motor, changeover valves are provided in the oil passages to respective cylinders, and intake and discharge cycles in each cylinder are carried out in synchronism with the rotation of crank shaft. Accordingly, such an hydraulic motor can be rotated continuously at a certain speed by the action of hydraulic cylinders however, it is not possible to rotate the crank shaft intermittently for respective controlled angles. In distinction to such continuously rotating hydraulic motors requiring this synchronism with the crank shaft, the present invention employs externally operated changeover valve means selectively operable independent of such a synchronism.